The invention relates to a process for the purification of salt-charged waste water by wet oxidation of organic constituents under super-critical conditions and also a reactor for performing the process.
U.S. Pat. No. 4,822,497 discloses such a process, a so-called SCWO process (SCWO=SuperCritical Water Oxidation). The reaction takes place in a vertically erected, cylindrical pressure vessel. A semi-critical or supercritical mixture of waste water, fuel and oxygen is supplied through a nozzle axially protruding from above into the reactor. After the reaction the hot fluid is drawn off with the reaction products in the upward direction. During the reaction salt precipitates abruptly in the form of small crystals (size in the micrometer range) and is partly deposited at the bottom of the reactor in a subcritical region, where it is removed by means of cold water as brine or a solid-brine mixture.
In a further development of this SCWO process (by ABB-LummusCrest) with a falling film of cooling water in the lower reactor section it is ensured that the salt does not become baked onto the reactor wall. Of course in the upper section salt can become deposited on the reactor wall and thus in time result in obstructions. The SCWO process is used in the disposal of process water which is difficult to or impossible to decompose biologically (e.g. in paper production). Amongst others, the process is particularly suitable for destroying dangerous substances such as dioxines, furanes, polychlorinated biphenyls (PCB), and warfare agents.
In the SCWO processes one is confronted with two main problems: Firstly the solubility of salts strongly decreases in the region around the critical point of water, which results in the deposit of salts and finally in obstructions. Secondly very corrosive conditions result because of the presence of salt at elevated temperatures.